Open-weight model GLM 5.3 builds a complete Firefox exploit chain within 48 hours without human intervention
Open-weight model GLM 5.3 built full Firefox exploit chains with zero human input in under 48 hours
Epoch AI researchers demonstrated that the Chinese open-weight model GLM 5.3 can exploit the window between when a security patch is made public and when users receive the update to attack Firefox users, at an API cost of about 1000 USD per successful attack. Across 6 Firefox versions released between September 17 and October 26, after receiving basic instructions the model autonomously identified upcoming security fixes, selected vulnerabilities and built multi-stage exploit chains, succeeding in as little as 12 hours; the web pages it built could read local files when loaded by a user and send them to an attacker's server, and each attempt independently rediscovered the same previously unknown sandbox bypass vulnerability. Guardrails from API providers including Z.ai did not trigger a refusal; the team disclosed the issue to Mozilla, and the relevant vulnerability was fixed in Firefox 159.0, released on October 27, 2026. Using the same method against Chrome cost about 100,000 USD and still did not yield an equivalent exploit chain, but the researchers cautioned that this does not mean Chrome is immune.
An open-weight model autonomously completed a real browser exploit chain at a cost of about 1,000 US dollars, which software vendors can use to examine the structural risks during the patch window.